1. Field of the Invention
This invention relates to a control method of optical cutting. It is performed as follows: first analyze the thermal stress distribution along a cutting path with a numerical analysis method, and then balance the undesired thermal stress with auxiliary heat sources.
2. Description of the Prior Art
Glass, ceramic materials, and such brittle materials are often used in many products or electronic apparatuses. For a flat panel display, a glass substrate is an important component thereof and is usually cut by means of mechanical machining or laser.
Cutting glass by means of mechanical machining is mostly performed with diamond wheel cutter and high-hardness metal wheel cutter. The processing includes three steps: carving, cleaving and grinding. Firstly, on the surface of glass, carve the line of desired shape to generate crack, then apply mechanical load on the crack to cleave the glass, and finally grind the edge of the cleaved glass to remove the swarf. Therefore, the method of mechanical glass cutting is much more complicated due to the more requirement of equipment, processing time, and labor cost. Additionally, the cutting edge is not smooth and has tiny cracks. The problems of residual stress and tiny pieces of swarf make the mechanical machining not conducive to large-size glass cutting. However, the above defects will not appear if a proper laser is applied for the glass cutting.
As the technique of laser develops, the laser sources are currently classified into two classes. One is that the laser could be absorbed by the work piece; the other is that the laser could penetrate the work piece. In addition, the glass cutting thereof is also classified into two classes: thermal melting method and thermal cracking method. Adopting the thermal melting method, the processing zone temperature is quite high and the cutting surface is not good. However, if the thermal cracking method is adopted, the processing zone temperature is low relatively, but it is still not easy to control the cutting surface.
The thermal cracking means that the thermal stress is used to generate cracking. It is valued because there is less swarf and less following work. The heat source generating thermal stress is usually a laser. There are various laser sources for glass cutting on the market, such as CO2 gas laser, Nd—YAG solid-state laser, Yb—YAG solid-state laser and so on. Because of the different wavelengths thereof, the extents of energy of different lasers absorbed by material are also different. The induced stress fields are therefore quite various. Furthermore, the sensitive relation between the stress field and the processing condition is the main reason why the cutting control is not easy. The common defects of thermal crack cutting are: the deviation of cutting path near the edge of work piece, the asymmetrical cutting of thick work piece with slant, staged, bumpy cutting surface, the non-accomplishable processing for closed path cutting, and so on. In practical application, if the work piece is not of flat cutting surface or not coincident with the desired shape, it will result in product disposal and thus increase the processing time and the product cost.
Therefore, the invention provides a control method of optical cutting. A thermal crack cutting path (cutting path for short) of a work piece is determined first. The thermal stress distribution of non-cracked work piece is obtained by analysis. The work piece is then irradiated along the cutting path with auxiliary heat sources so as to eliminate the undesired thermal stress of non-cracked work piece. It thus makes the actual cutting be coincident with the predetermined cutting path, increases the yield of product and further improves the quality of cutting surface.